1. Field of the Invention
The present invention relates to a plasma generator. More particularly, the present invention relates to a plasma generator which combines an inductively coupled plasma (ICP) generator and a surface wave plasma generator.
2. Description of the Prior Art
Plasma is a partially ionized gas, and has been widely applied to semiconductor processes, such as deposition, etching, ion implantation and surface treatment. In the application of plasma in the etching process, there are three main mechanisms: one is using partical bombardment with physical behavior; another is to decompose moleculars to reactive ions for thin film by plasma, then an etching process is proceeded with drawing the volatile product out by a vacuum system, which is produced by the reaction between the ions and the thin film; the other is to proceed etching process by combining the physical and chemical removing thin film mechanism.
If the etched thin film is metal, the main plasma etching gases are Cl2 and BCl3. Cl ions made from Cl2 react with metal to form volatile metal chloride so as to etch the metal layer. The size of the ions produced by traditional ICP generator is smaller, and the main ion is Cl+. A higher aspect ratio and a higher electron temperature are obtained when the metal layer is etched by the above-mentioned plasma. However, higher electron temperature will waste photoresist, therefore, thicker photoresist is requested to prevent distortion. If the metal layer is etched by the plasma generated by surface wave plasma generator, a lower electron temperature is obtained. Then, the photoresist will not be wasted too much, and the thickness of that can be reduced. However, the size of the ions, such as BCl2+, BCl3+ and BCl+, produced by the surface wave plasma generator is too big to obtain higher aspect ratio when etching the metal layer.
With the linewidth getting smaller and the integration larger, how to reduce the thickness of the photoresist to enhance the resolution in exposure process and increase the aspect ratio between metal lines to enhance the integration have become increasingly important.
An object of the present invention is to provide a plasma source to etch the metal layer without wasting photoresist and with getting higher aspect ratio.
Another object of the present invention is to provide a plasma generator which combines the advantages of the ICP generator and surface wave plasma generator.
Another object of the present invention is to provide a plasma generator which can adjust the ratio of bigger ions and smaller ions.
The present invention provides a plasma generator, comprising an ICP chamber and a surface wave conducting device. The ICP chamber having a quartz plate as an upper wall and an electrode coupled to a RF bias supply in the lower ICP chamber is used to produce a first plasma. The surface wave conducting device is located on the quartz plate and used to produce a second plasma in the upper ICP chamber. Then, the first plasma and the second plasma are mixed together inside the ICP chamber.
The present invention provides a plasma generator, suitable for etching a thin film on a wafer, comprising an ICP chamber and a surface wave conducting device. The ICP chamber having a chamber wall, a coil surrounding the chamber wall and a gas inlet on the chamber wall, a quartz plate as an upper wall, and an electrode coupled to a RF bias supply in the lower ICP chamber is used to produce a first plasma. A gas source is introduced through the gas inlet to the ICP chamber. The surface wave conducting device is located on the quartz plate and used to produce a second plasma in the upper ICP chamber. Then, the first plasma and the second plasma are mixed together inside the ICP chamber.
According to the preferred embodiment of the present invention, a lot of slots are located on one side of the surface wave conducting device near the quartz plate.